Antimicrobial synergism of silver and zinc oxide nanoparticles with antibiotics against clinical isolate of Cutibacterium acnes.

BACKGROUND

The need to develop alternative treatment approaches to acne vulgaris and other skin infections is becoming increasingly urgent due to the rising prevalence of antibiotic resistance in Cutibacterium acnes (a key pathogen related to such conditions). Nanoparticles (NPs) have shown great potential as antimicrobial agents that could improve the effectiveness of traditional antibiotics when administered together. This research examines antibacterial activity of silver NPs (Ag-NPs) and zinc oxide NPs (ZnO-NPs), both independently and when used collaboratively with common anti-acne antibiotics used to treat C. acnes.

METHODS

Ag-NPs and ZnO-NPs were biosynthesized using aqueous Peganum harmala extract as a reducing and stabilizing agent. The synthesized nanoparticles were characterized using UV-Vis spectroscopy, X-ray diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), and dynamic light scattering (DLS). This research examined two C. acnes clinical isolates (P1 and P2) and one reference strain (NCTC747) were used in this research. Broth microdilution assays were employed to determine minimum inhibitory concentrations (MICs). Checkerboard assays and fractional inhibitory concentration index (FICI) analysis were performed to explore synergy between antibiotics and NPs.

RESULTS

A successful formation of spherical Ag-NPs and hexagonal ZnO-NPs has been confirmed, with average crystallite sizes of approximately 13-14 nm and 53-55 nm, respectively. Both Ag-NPs and ZnO-NPs were found to exhibit strong antibiotic activity. The MICs of the tested antibiotics were significantly reduced when used in combination with AgNPs. The reduction was up to 2-8 fold compared to antibiotic monotherapy. Moreover, most Antibiotic-Ag-NPs combinations exhibited synergistic interactions in the FICI analysis (FICI ≤ 0.5). Meanwhile, there are increased moderate effects resulted from the ZnO-NP combinations. The Antibiotic MIC generally values reduced two-to-four-fold. The relevant FICI values suggested that the interactions were primarily additive (FICI ≈ 0.75), although there was some evidence of strain-dependent variations. A two-way ANOVA test showed that the MIC values reductions for both antibiotics and nanoparticles were statistically significant (p < 0.001).

CONCLUSION

The potential of biosynthesized NPs as adjunct therapeutic agents for the management of acne-associated infections was suggested by their promising antibacterial and antibiotic-enhancing effects against C acnes.